Control of emissions from motor vehicles is now an accepted and necessary automotive design consideration throughout the world. In the United States since about 1965 (and earlier in California) all motor vehicles sold have incorporated some form of emission control. Recently, more vehicles sold for use in countries other than the United States have also been designed to reduce pollutants. The speed with which engine design changes have taken place to satisfy pollution reduction requirements has been extraordinary. Not only have the engine and vehicle manufacturers had to engage in major expenditures for facilities, equipment, and accelerated technical achievement, but similarly, the automotive service industry has been experiencing a major upheaval in the effort to provide continuing emission control apparatus malfunction diagnosis and maintenance capability.
The stringent standards in the United States for 1975 have forced most automobile manufacturers to use catalytic converters on current production vehicles to provide adequate control of exhaust emissions of hydrocarbons (HC) and carbon monoxide (CO). When the catalytic converter is functioning properly, it oxidizes essentially all of the HC and CO to carbon dioxide (CO.sub.2) and water vapor (H.sub.2 O). Oxygen (O.sub.2) concentrations and the source of O.sub.2 in the exhaust gas (i.e., from secondary air pumps or through modulated air bleeds to the induction system) necessary for the proper operation of the catalytic converter will become an important control and adjustment parameter in the design as well as in the proper servicing of vehicles in subsequent years. The service mechanic will be required to make precise adjustment of air control devices based upon exhaust concentrations of O.sub.2. Of course, the measurement of HC and CO will continue to be important tools as well, in the complete diagnosis of engines and emission control systems.
In the patent to J. D. Blanke and N. E. Brunell (U.S. Pat. No. 4,030,349) entitled ENGINE ANALYSIS APPARATUS and the patent to J. D. Blanke (U.S. Pat. No. 4,031,747) entitled MISFIRE MONITOR FOR ENGINE ANALYSIS HAVING AUTOMATIC RESCALING, assigned to the common assignee of this application, apparatus and methods are disclosed wherein the rate of change of O.sub.2 at the tailpipe with respect to time is used to properly adjust the carburetor settings of the engine so as to prevent a lean roll condition which would otherwise act to lower engine efficiency and raise pollutant output. Thus, it can be seen that the monitoring of oxygen content in the exhaust gases of automobiles is rapidly becoming an important diagnostic consideration.
Catalytic converters must operate at relatively high temperatures (450.degree. to 700.degree. C.) to accomplish efficient conversion of HC and CO to CO.sub.2 and H.sub.2 O. Through 1977 all catalytic converter equipped vehicles have utilized oxidizing catalysts (rather than reduction catalysts) which require free O.sub.2 to function. The catalyst, which may be either in the pellet or monolithic form, is usually a substrate of alumina or similar material coated with a small amount of platinum and/or palladium. The noble metal catalyzes an oxidation reaction in the presence of HC, CO and O.sub.2 to accomplish conversion to non-toxic products of complete combustion. The reactions are: EQU 2CO+ O.sub.2 .fwdarw. 2CO.sub.2 ; and, EQU 2H.sub.2 + O.sub.2 .fwdarw. 2H.sub.2 O.
if there is not enough O.sub.2 available, conversion efficiency suffers and, if there is an excess of O.sub.2 available, the catalyst assists in the conversion of gasoline sulfur to undesirable SO.sub.3 which ultimately forms H.sub.2 SO.sub.4 and other sulfates. The problem of the production of H.sub.2 SO.sub.4 by catalytic converter equipped automobiles is one of concern presently under study.
It is possible for the surface of the catalyst, wherein the above described catalytic reaction takes place, to become poisoned by metals such as lead which may be contained in the exhaust gases. As the catalyst becomes poisoned, the chemical activity of the catalyst becomes reduced. As the amount of chemical activity becomes less than that required for total reaction of the products in the exhaust stream, only a portion of the desired reaction can take place. The portion of the reaction taking place as compared to the total reaction which could take place in an unpoisoned catalytic converter is a measure of efficiency of the catalytic converter. That is, if only 50% of the reaction is taking place which would take place with an unpoisoned catalytic converter of the same configuration, the catalytic converter in question is 50% efficient. Since the engine is injecting air containing O.sub.2 into the exhaust stream in a quantity needed to oxidize the CO and HC's for high efficiency, with less than 100% efficiency the balance of the O.sub.2 will be passed through as free O.sub.2. Obviously, the HC and CO content of the exhaust gases as emitted into the atmosphere will also rise.
At such time as the efficiency of the catalytic converter drops below a minimum acceptable level, appropriate action needs to be taken in order to obtain the clean air benefits to the populus for which the catalytic converter was originally incorporated into the automobile. Either the catalytic converter should be replaced or, alternatively, it should be rejuvenated such as by the technique described in the copending application Ser No. 820,481 issued as U.S. Pat. No. 4,116,053 to R. M. Neti and K. B. Sawa for CATALYTIC REACTOR SYSTEMS METHOD AND APPARATUS, also assigned to the common assignee of the present application.
As with other forms of automobile exhaust emission testing any technique and apparatus for testing catalytic converter efficiency must be inexpensive, convenient, and rapid if it is going to be of practical value. Components of the exhaust system of an automobile are typically quite hot when presented to a service garage for analysis since the automobile is normally driven to the garage or tested following a tuneup as opposed to being tested in the owner's garage after a period of non-operation. Likewise, components of the automotive exhaust system are prone to rusting and the accompanying seizing of nuts and bolts used for assembly due to the action of the high temperatures in conjunction with the moisture in the exhaust, air, and from the road surfaces which tends to remove any protective coatings thereon and stimulate the oxidation of the ferrous materials from which the exhaust component housings are normally manufactured. Similar problems of heat and rusting were encountered when sampling ports for the insertion of gas sampling apparatus were installed in exhaust systems. Such sampling ports are, therefore, no longer included in automotive exhaust systems as manufactured. Consequently, any testing of the efficiency of a catalytic converter must be accomplished on the car, without removal therefrom, in the presence of components too hot to handle and without the benefit of a sampling port. Thus, what is needed is a technique for analyzing the efficiency of a catalytic converter equipped exhaust system wherein the only contact with the exhaust system itself is through a probe or sampling device inserted into the tailpipe to sample the quantity of one or more components of the gas stream.
Wherefore, it is the object of the present invention to provide a method for determining the efficiency of a catalytic converter equipped automotive exhaust system in situ which is rapid, accurate, simple, inexpensive, and convenient.